When I read the lyrics to "Numb," the scene in The Pursuit of Happyness that immediately came to mind was the scene with Gardner and his wife in the bathroom getting ready for work. In terms of proximity, they are within that intimate space, but mentally they are distant. Their relationship is strained because they are struggling financially. Chris has been unsuccessful in selling bone density scanners and his wife is working double-shifts. In the bathroom scene, Chris mentions that he is going to see about a stock broker internship. His wife chastises him because she is fed up with their situation and thinks Chris is being impractical. She makes some comment, which I can't quite remember. It is something to the effect of, "Why don't you just apply to be an astronaut?!"
Camera angles are important here. The couple are looking in the mirror. Chris is attempting to better himself and his wife mocks him. The use of the mirror is important in that they both are looking at themselves and at each other, who they are as individuals and a couple and who they might want to be. You could interpret it both ways. Chris is smothered by his wife or she is smothered by his insistence on taking risks: density scanner and the seemingly unlikelihood of Chris becoming a stock broker. Both Chris and his wife are numb, tired. But the lyrics in the song do seem to be a bit more applicable to Chris since he is mocked for doing what he thinks is best. "Every step that I take is another mistake to you."
The composer of the song "Numb" expresses his inability to belong. He could be speaking to a lover, his parents, a group or society in general. You can use the perspective of Chris or his wife. Since Chris is the main character, I'll use him. Chris experiences increasing difficulty belonging in his relationship with his wife. He refuses to belong to the social class he is currently in. His pursuit of happiness is the pursuit of the ability and opportunity to belong somewhere else. This is the possible, yet illusive American Dream: that anyone can achieve anything through hard work. The speaker in "Numb" wants to belong but feels forced to be someone he's not. Chris realizes he no longer belongs with his wife and is on a quest to belong somewhere else.